Polyvinyl chloride is one of the most widely used plastics in the world, and is present in such applications as pipes and pipe fittings, film and sheet, flooring, cables and construction profiles. However, polyvinyl chloride can decompose during processing, upon heating or on prolonged exposure to sunlight due to loss of HCl from the polymer, resulting in discoloration and embrittlement. Stabilizers are used to prevent or reduce degradation and discoloration of polyvinyl chloride due to its exposure to heat, UV-light and in-process stress and shear that cause dehydrochlorination, auto-oxidation and mechano-chemical chain scission of the polymer and its co-polymers. These stabilizers help to prevent degradation not only during processing of the polyvinyl chloride compound, but also during the useful life of finished goods and articles made from it. Driven by the importance of stabilizer performance in compounds containing polyvinyl chloride, work has been ongoing to produce improved stabilizers for such use.
U.S. Pat. No. 2,669,548 relates to stabilizers containing zinc salts of organic or inorganic acids, calcium ethyl acetoacetate and 1,3-dicarbonylic compound, such as beta-diketones.
U.S. Pat. No. 2,711,401 relates to stabilizers containing admixtures of metal carboxylates of aliphatic and cycloaliphatic acids, where the metal is Mg, Ca, Sr, Ba, Zn or Cd, among others, with aliphatic polyhydric alcohols, esters of aliphatic polyhydric alcohols or ethers of aliphatic polyhydric alcohols.
U.S. Pat. No. 3,003,998 relates to stabilizer compositions consisting of calcium benzoate, zinc salts of fatty acids and glycerol.
U.S. Pat. No. 3,003,999 describes stabilizer compositions consisting of calcium salts of fatty acids, zinc salts of fatty acids and sorbitol.
U.S. Pat. No. 3,004,000 relates to stabilizer compositions consisting of calcium and zinc salts and sorbitol, where at least one of the salts is benzoate and at least of the salts is derived from fatty acids.
U.S. Pat. Nos. 4,123,399 and 4,123,400 relate to rigid and plasticized PVC homo- or co-polymer compounds stabilized with a mixed metal stabilizer, a polyol (such as sorbitol) and a beta-diketone (such as dibenzoylmethane and stearoylbenzoylmethane). The mixed metal stabilizer comprises aromatic and aliphatic carboxylates of calcium, zinc, barium and cadmium, including salts of fatty acids.
U.S. Pat. No. 4,421,687 relates to a PVC stabilizer comprising at least one basic inorganic compound of lithium, sodium, potassium, magnesium, calcium, strontium, or barium, among other metals and a 1,3-deketone.
U.S. Pat. No. 5,451,628 relates to a stabilizer consisting of a mixed zinc/alkaline-earth metal carboxylate, a hydrotalcite and antimony trioxide, where the mixed metal carboxylate is selected from the group consisting of barium/zinc carboxylate and calcium/zinc salts of fatty acids.
Plasticizers are used primarily in flexible and semi-rigid polyvinyl chloride compounds to improve their processability, flexibility, durability and stretchability, decrease melt viscosity, glass transition temperature, and modulus of elasticity. Bio-based plasticizers additionally may result in a positive environmental impact including reduced carbon footprint and reduced energy consumption.
In view of the need for flexible polyvinyl chloride compounds that are environmentally friendly, work has also been ongoing to develop bio-based plasticizers derived from fatty acids and containing epoxy functional groups.
U.S. Pat. No. 2,895,966 relates to the preparation of predominantly epoxidized monoglyceride diacetates by trans-esterifying vegetable oils with triacetin (glycerol triacetate).
U.S. Pat. No. 3,049,504 relates to a process for the preparation of an epoxidized monoglyceride diacetate-type plasticizer, where animal fat is used as a raw material.
U.S. Pat. No. 6,797,753 relates to compositions and methods for plasticizing polyvinyl chloride polymers where the plasticizers contain fatty acids derived from vegetable oils and the fatty acids are substantially fully esterified with an alcohol (mono-ol or polyol), the fatty acids having unsaturated bonds that are substantially fully epoxidized, and wherein the fatty acids are added substantially randomly to one or more hydroxyl sites on the alcohol. The plasticizers may be added in amounts between about 10 to 230 phr of PVC resin.
U.S. Pat. No. 8,383,708 relates to unhindered polyols used to react with an epoxidized soyate to make epoxidized soyate diester in the presence of a catalyst. The unhindered polyol can be 1,3-propanediol or any polyol having four or more carbon atoms with no two adjacent carbon atoms having hydroxyl functionality. A combination of catalysts is used to promote the transesterification reaction of the epoxidized soyate with the unhindered polyol to yield a high percentage of epoxidized soyate diester with epoxy functionality retained. The primary catalyst is a metallic hydroxide, and the secondary catalyst is a titanate. Bioderived epoxidized soyate diester plasticizers useful for thermoplastics and thermosets result.
U.S. Patent Application No. 2010/0010126 relates to the use of an inter-esterification reaction between vegetable or animal oils as monoacid esters (preferentially with 1 to 12 carbons) and monoalcohol esters (preferentially with 1 to 12 carbons). The use of ethyl acetate is preferred as it is a product that may be obtained from ethanol (renewable) and has a boiling point (77 deg. C.), which facilitates separation by vacuum distillation at the end of the reaction and its reuse. By varying the molar ratio between glycerol triester (oil or fat) and monoalcohol ester, different proportions of glycerol esters are obtained with 1 or 2 linked fatty acids and 1 or 2 linked acids of short chain, along with the formation of fatty acid ester and monoalcohol ester. After the distillation of excess residual ethyl acetate, products are obtained with a viscosity from 21 to 33 cPs at 25° C. in the case of the reaction with soy oil.
U.S. Patent Application Publication No. 2010/0010127 relates to bioplasticizers or primary oleochemical plasticizers and the improved process for obtaining them. It refers primarily to epoxidized oleochemical plasticizers produced from vegetable oils as a substitute for traditional petrochemical plasticizers.
U.S. Pat. No. 7,071,343 relates to epoxidized glyceride acetates made by a process which comprises reacting an epoxy fatty acid ester and triacetin.
WO2011/143028 relates to PVC resin-based compositions that include biochemical plasticizers as the primary plasticizers. The compositions include PVC resin, a compatibilizer, one or more biochemical plasticizers and, optionally, a thermoplastic elastomer impact modifier. The biochemical plasticizers are present in substantial quantities in the compositions and, in some embodiments, are the only plasticizers present in the compositions.
WO2013/055961 relates to plasticizer compositions comprising epoxidized fatty acid mono-esters and epoxy-esters.
Nevertheless, a continuing need exists for systems that provide improved stability and flexibility in PVC products. In particular, there is a need for PVC/stabilizer/plasticizer systems that minimize adverse environmental impact. Certain conventional phthalate plasticizers have a large carbon footprint, and present potential toxicological concerns to consumers. Additionally, conventional mixed metal stabilizers have Ba/Zn and Ca/Zn atomic ratios of between 1 to 3 and 0.33 to 1, respectively (Handbook of Polyvinyl chloride formulating; edited by Edward J. Wickson; John Wiley & Sons, 1993, p. 322-325). However, there is a growing sentiment to restrict or reduce certain mixed metal stabilizes designated as hazardous. Metals that are currently under the regulatory pressure include cadmium and lead, and to a certain extent barium and zinc. Reduction in the total metal content may also lead to improving certain performance characteristics of plasticized PVC, such as plasticizer permanence. Therefore, reducing the total metal content of both mixed metal stabilizers and flexible PVC compounds is critical for reducing amount of potentially hazardous chemicals in use as well as improving performance of the final articles.
It has unexpectedly been discovered that flexible PVC compounds having improved stability and reduced environmental impact can be produced using a low metals content mixed metal stabilizer system and at least one bio-based primary plasticizer comprising epoxidized fatty acid esters.